Fix Asyncify in the d8 shell (#16340)

This is similar to the Node.js path. This code is necessary
for us to throw an exception to stop execution, but keep going after it is
caught, rather than call d8's quit which halts us immediately.

Also remove some misleading annotations on tests. d8 does have setTimeout,
despite what the comments say - but perhaps it didn't in the past.

Author: kripken

src/shell.js

@@ -309,6 +309,20 @@ if (ENVIRONMENT_IS_SHELL) {
 
   if (typeof quit == 'function') {
     quit_ = (status, toThrow) => {
+      // Unlike node which has process.exitCode, d8 has no such mechanism. So we
+      // have no way to set the exit code and then let the program exit with
+      // that code when it naturally stops running (say, when all setTimeouts
+      // have completed). For that reason we must call `quit` - the only way to
+      // set the exit code - but quit also halts immediately, so we need to be
+      // careful of whether the runtime is alive or not, which is why this code
+      // path looks different than node. It also has the downside that it will
+      // halt the entire program when no code remains to run, which means this
+      // is not friendly for bundling this code into a larger codebase, and for
+      // that reason the "shell" environment is mainly useful for testing whole
+      // programs by themselves, basically.
+      if (runtimeKeepaliveCounter) {
+        throw toThrow;
+      }
       logExceptionOnExit(toThrow);
       quit(status);
     };

tests/test_core.py

@@ -26,7 +26,7 @@
 from common import RunnerCore, path_from_root, requires_native_clang, test_file, create_file
 from common import skip_if, needs_dylink, no_windows, no_mac, is_slow_test, parameterized
 from common import env_modify, with_env_modify, disabled, node_pthreads
-from common import read_file, read_binary, require_node, require_v8
+from common import read_file, read_binary, require_v8
 from common import NON_ZERO, WEBIDL_BINDER, EMBUILDER
 import clang_native
 
@@ -7613,8 +7613,6 @@ def test_setlocale(self):
   def test_vswprintf_utf8(self):
     self.do_run_in_out_file_test('vswprintf_utf8.c')
 
-  # needs setTimeout which only node has
-  @require_node
   @no_memory64('TODO: asyncify for wasm64')
   def test_async_hello(self):
     # needs to flush stdio streams
@@ -7640,7 +7638,11 @@ def test_async_hello(self):
 
     self.do_runf('main.c', 'HelloWorld!99')
 
-  @require_node
+  @require_v8
+  @no_memory64('TODO: asyncify for wasm64')
+  def test_async_hello_v8(self):
+    self.test_async_hello()
+
   @no_memory64('TODO: asyncify for wasm64')
   def test_async_ccall_bad(self):
     # check bad ccall use
@@ -7672,7 +7674,6 @@ def test_async_ccall_bad(self):
     self.emcc_args += ['--pre-js', 'pre.js']
     self.do_runf('main.c', 'The call to main is running asynchronously.')
 
-  @require_node
   @no_memory64('TODO: asyncify for wasm64')
   def test_async_ccall_good(self):
     # check reasonable ccall use